Added support for LOAD_CLASSDEREF

The opcode itself is exactly the same as `LOAD_DEREF`
1) The problem is when the class is a closure (e.g. defined inside a function body) then there is a `BUILD_TUPLE` after the `LOAD_BUILD_CLASS` which makes problems.
2) There is another problem which makes the `code->name()` of the class to be part of the function locals. (e.g. `func.<locals>.my_class` instead of `my_class`) which makes the check `srcString->isEqual(code->name().cast<PycObject>())` be invalid.

tests/input/load_classderef.py

@@ -0,0 +1,4 @@
+def func():
+	x = 1
+	class my_class:
+		y = x